Current collector and preparation method therefor, electrode sheet, secondary battery, and electric device

Abstract

Disclosed are a current collector and a preparation method therefor, an electrode sheet, a secondary battery, and an electric device. The current collector comprises an electroplated copper foil. Under test conditions of a temperature of 10-30°C, a sample length × width of (50±0.25 mm)×(15±0.25 mm), and a stretching speed of 50±0.5 mm / min, the yield-strength ratio of the copper foil is 0.55-0.75, and the elongation at break thereof is 5.5-7.5%. The current collector comprises the electroplated copper foil, which has good tensile and elongation properties, and thus, the bending resistance of the copper foil is significantly improved, such that copper foil fractures during the winding process of the electrode sheet can be reduced or avoided, thereby reducing the potential safety hazard of a secondary battery.

Description

Current collectors and their preparation methods, electrodes, secondary batteries and electrical devices

[0001] Cross-referencing

[0002] This application incorporates Chinese Patent Application No. 202411059645.2, filed on August 2, 2024, entitled “Current collector and preparation method thereof, electrode, secondary battery and power device”, which is incorporated herein by reference in its entirety. Technical Field

[0003] This application relates to the field of secondary battery technology, and in particular to a current collector and its preparation method, an electrode, a secondary battery, and an electrical device. Background Technology

[0004] With the widespread application of secondary batteries in energy storage power systems such as hydropower, thermal power, wind power and solar power plants, as well as in many fields such as power tools, electric bicycles, electric motorcycles, electric cars, military equipment, and aerospace, the market's requirements for high energy density, high safety and low cost of secondary batteries are constantly increasing. The trend of battery current collectors becoming extremely thin has become a trend, which puts forward higher requirements for the mechanical performance of current collectors.

[0005] As the thickness of the current collector decreases, its mechanical strength diminishes, failing to meet market demands for high energy density, high safety, and low-cost rechargeable batteries. Therefore, it is necessary to provide a current collector with excellent mechanical properties to meet the requirements of next-generation rechargeable batteries for ultra-thin current collectors. Summary of the Invention

[0006] This application provides a current collector and a method for preparing the same, as well as an electrode including the current collector, a secondary battery, and an electrical device. The current collector includes an electroplated copper foil with good tensile and elongation properties. The copper foil has significantly improved bending resistance, which can reduce or avoid copper foil breakage during electrode winding and reduce the safety hazards of the secondary battery.

[0007] An embodiment of the first aspect of this application provides a current collector comprising electroplated copper foil. Under test conditions of 10℃-30℃, sample length × width of (50±0.25mm) × (15±0.25mm), and tensile speed of 50±0.5mm / min, the copper foil exhibits a yield strength ratio of 0.55-0.75 and an elongation at break of 5.5%-7.5%. The copper foil possesses both good tensile strength and elongation at break, demonstrating excellent mechanical strength and plasticity.

[0008] In some embodiments, the copper foil has a yield strength ratio of 0.55-0.72 and / or an elongation at break of 5.5%-7.3%. The copper foil can further improve mechanical strength and plasticity, reduce brittleness, and enhance deformation stability.

[0009] In some embodiments, the tensile strength of the copper foil is 500 MPa-650 MPa. In other embodiments, the tensile strength of the copper foil is 510 MPa-610 MPa. Tensile strength within this range helps improve the mechanical strength of the copper foil, making it suitable for high-energy-density secondary batteries.

[0010] In some embodiments, the maximum and minimum grain size of the copper foil grains spans between 2 μm and 4 μm. In some embodiments, the maximum and minimum grain size of the copper foil grains spans between 2.3 μm and 3 μm.

[0011] Copper foil with a larger grain size distribution further increases the number of geometrically necessary dislocations, increases the grain dislocation density, enhances the resistance to grain dislocation movement and reduces the occurrence of concentrated stress during copper foil deformation, thereby improving the mechanical strength of the copper foil while also improving deformation stability.

[0012] In some implementations, the copper foil satisfies at least one of the following conditions:

[0013] (1) The average grain size of the copper foil is 0.2μm-0.7μm;

[0014] (2) The minimum grain size of the copper foil is 0.1μm-0.3μm;

[0015] (3) The maximum grain size of copper foil is 2μm-4μm.

[0016] Different grain sizes in copper foil exhibit varying work hardening capabilities due to differences in grain boundary density, thus resulting in varying mechanical strengths and bending resistance. Different grain sizes in copper foil can enhance the work hardening differential, strengthen the ability to suppress strain localization, reduce stress concentration, and improve both the mechanical strength and brittleness of the copper foil. Furthermore, variations in grain size can induce a higher density of geometrically necessary dislocations, increasing the resistance to grain slip and improving the plasticity of the copper foil. This results in copper foil possessing both good deformation stability and bending resistance, ultimately improving the safety and lifespan of secondary batteries.

[0017] In some embodiments, the copper foil has a thickness of 4μm-8μm. This thin and lightweight copper foil helps reduce battery weight and further increase energy density.

[0018] The second aspect of this application provides a method for preparing a current collector, including an electroplating method for preparing electroplated copper foil. The electroplating method includes applying a linear oscillating current to an electrolyte to reduce and deposit copper ions in the electrolyte to form copper foil. Under test conditions of 10℃-30℃, sample length × width of (50±0.25mm) × (15±0.25mm), and tensile speed of 50±0.5mm / min, the yield strength ratio of the copper foil is 0.55-0.75 and the elongation at break is 5.5%-7.5%.

[0019] The preparation method is mature, requires little equipment, and has low manufacturing cost. The prepared copper foil not only has excellent mechanical strength and good deformation stability, but also helps to reduce the manufacturing cost of secondary batteries.

[0020] In some implementations, the linear oscillating current of the electroplating method varies in the range of 20KA-45KA.

[0021] In some implementations, the period of the linear oscillating current in the electroplating process is 10ms-500ms.

[0022] The magnitude of the current can control the deposition rate of copper ions, and the grain size in the copper foil can be adjusted by varying the range of the linear oscillating current. Grain sizes of different dimensions are beneficial for increasing the grain boundary density and geometrically necessary dislocations in the copper foil, mitigating the grain boundary tortuosity degradation caused by reduced grain size, strengthening the copper foil's strength and improving its bending resistance, and mitigating brittle defects caused by fine-grain strengthening. The current variation period can adjust the grain size range between the largest and smallest grains in the copper foil, which is beneficial for grains of different sizes to fully accumulate geometrically necessary dislocations and increase the ability to suppress local strain, thereby improving the mechanical strength of the copper foil while enhancing its deformation stability.

[0023] In some embodiments, the distance between the cathode electrode and the anode electrode in the electroplating process is 10mm-20mm.

[0024] In some embodiments, the electroplating deposition temperature is 40°C-60°C.

[0025] In some implementations, the electroplating deposition time is greater than or equal to 80 seconds.

[0026] Adjusting electroplating parameters helps to prepare copper foil with regular grains and appropriate thickness, thus improving the quality of copper foil.

[0027] In some embodiments, the electrolyte comprises:

[0028] Leveling agents, including collagen;

[0029] Wetting agents, including one or more of polyethylene glycol and hydroxyethyl cellulose;

[0030] Brighteners, including sodium polydithiopropane sulfonate.

[0031] In some embodiments, the brightener includes sodium polydithiopropane sulfonate.

[0032] Leveling agents in the electrolyte can adhere to the tips of copper foils with high deposition rates, inhibiting grain growth, balancing the growth rates of pits and tips, and improving the flatness of the copper foil. Wetting agents improve the wettability between the electrolyte and the substrate; the wettability of the electrolyte on the cathode is sufficient to enable rapid electrodeposition with high current, increasing the nucleation rate of the copper foil and reducing the grain size. Brighteners further refine the grain size of the copper foil, reduce surface roughness, and improve surface smoothness.

[0033] In some embodiments, the electrolyte comprises: collagen at a concentration of 10-300 mg / L, polyethylene glycol at a concentration of 20-100 mg / L, hydroxyethyl cellulose at a concentration of 10-100 mg / L, and sodium polydisulfide dipropane sulfonate at a concentration of 50-200 mg / L.

[0034] In some embodiments, the electrolyte comprises: collagen at a concentration of 90-120 mg / L, polyethylene glycol at a concentration of 20-80 mg / L, hydroxyethyl cellulose at a concentration of 10-80 mg / L, and sodium polydisulfide dipropane sulfonate at a concentration of 50-150 mg / L.

[0035] In some embodiments, the electrolyte includes chloride ions at a concentration of 10-100 mg / L and copper ions at a concentration of 60-100 g / L, which can further improve the electrodeposition process.

[0036] The preparation method helps to form a dense, flat copper foil with continuously varying grain size. This copper foil has excellent yield strength ratio and elongation at break, significantly improved tensile strength and bending resistance, good mechanical strength and deformation stability, which is beneficial to improving the safety performance of high energy density or high expansion batteries.

[0037] An embodiment of the third aspect of this application provides an electrode comprising a current collector according to any embodiment of the first aspect of this application or a current collector prepared by any method according to any embodiment of the second aspect of this application. The current collector comprises copper foil, which enhances the mechanical strength of the copper foil, reduces brittle defects caused by direct current deposition of the copper foil, and improves the deformation stability of the copper foil. This makes it suitable for secondary batteries with high expansion force, which is beneficial for further improving the energy density of secondary batteries.

[0038] An embodiment of the fourth aspect of this application provides a secondary battery, including the electrode sheet of any embodiment of the third aspect of this application.

[0039] The fifth aspect of this application provides an electrical device including a secondary battery according to any embodiment of the fourth aspect of this application. Attached Figure Description

[0040] Figure 1 is a schematic diagram of a secondary battery according to an embodiment of this application;

[0041] Figure 2 is an exploded view of a secondary battery according to an embodiment of this application shown in Figure 1;

[0042] Figure 3 is a schematic diagram of a battery module according to an embodiment of this application;

[0043] Figure 4 is a schematic diagram of a battery pack according to an embodiment of this application;

[0044] Figure 5 is an exploded view of the battery pack of one embodiment of this application shown in Figure 4;

[0045] Figure 6 is a schematic diagram of an electrical device using a secondary battery as a power source according to an embodiment of this application.

[0046] Figure 7 shows a schematic diagram of the current change during the preparation of copper foil according to an embodiment of this application;

[0047] Figure 8 shows the stretch curve of the copper foil of Embodiment 1 of this application;

[0048] Figure 9 shows the stretch curve of the copper foil in Embodiment 2 of this application;

[0049] Figure 10 shows the stretch curve of the copper foil of Embodiment 3 of this application;

[0050] Figure 11 shows the stretch curve of the copper foil of Embodiment 4 of this application;

[0051] Figure 12 shows the stretch curve of the copper foil of Embodiment 5 of this application;

[0052] Figure 13 shows the stretch curve of the copper foil of Comparative Example 1 of this application;

[0053] Figure 14 shows the inverse pole figure distribution of the copper foil of Embodiment 1 of this application using an electron backscatter diffraction (EBSD) spectrometer.

[0054] Figure 15 shows the particle size distribution of the copper foil of Embodiment 1 of this application as determined by electron backscatter diffraction (EBSD).

[0055] Figure 16 shows the inverse pole figure distribution of the copper foil of Embodiment 2 of this application using an electron backscatter diffraction (EBSD) spectrometer.

[0056] Figure 17 shows the particle size distribution of the copper foil of Example 2 of this application, as determined by electron backscatter diffraction (EBSD).

[0057] Figure 18 shows the inverse pole figure of the copper foil of Comparative Example 1 of this application using an electron backscatter diffraction (EBSD) spectrophotometer.

[0058] Figure 19 shows the particle size distribution of the copper foil of Comparative Example 1 of this application, as determined by electron backscatter diffraction (EBSD).

[0059] Explanation of reference numerals in the attached diagram: 1 Battery pack; 2 Upper housing; 3 Lower housing; 4 Battery module; 5 Secondary battery; 51 Housing; 52 Electrode assembly; 53 Cover plate. Detailed Implementation

[0060] The following detailed description, with appropriate reference to the accompanying drawings, discloses embodiments of the positive electrode active material, its manufacturing method, positive electrode sheet, secondary battery, battery module, battery pack, and electrical device of this application. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided for the purpose of enabling those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0061] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0062] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0063] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0064] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0065] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0066] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0067] Typically, a secondary battery includes a positive electrode, a negative electrode, an electrolyte, and a separator. During charging and discharging, active ions (e.g., lithium ions, sodium ions) move back and forth between the positive and negative electrodes, inserting and extracting. The electrolyte acts as a conductor for the active ions between the positive and negative electrodes. The separator, located between the positive and negative electrodes, primarily prevents short circuits while allowing active ions to pass through. The negative electrode includes a negative current collector, which restrains cell expansion to prevent the anode from breaking during cycling.

[0068] As market demand for battery energy density increases, the mechanical strength requirements for current collectors, especially negative electrode current collectors, in rechargeable batteries are also rising to reduce safety hazards. Current technologies typically improve the mechanical strength of current collectors by refining grains to increase grain boundary density and dislocation movement resistance. However, grain refinement reduces grain boundary tortuosity, causing intergranular fracture of the current collector under bending or stress, resulting in high brittleness. This makes the inner electrode sheets of the cell extremely prone to breakage, creating safety hazards.

[0069] [current collector]

[0070] Based on this, an embodiment of the first aspect of this application provides a current collector comprising electroplated copper foil. Under test conditions of 10℃-30℃, sample length × width of (50±0.25mm) × (15±0.25mm), and tensile speed of 50±0.5mm / min, the copper foil exhibits a yield strength ratio of 0.55-0.75 and an elongation at break of 5.5%-7.5%. With the yield strength ratio and elongation at break within these ranges, the current collector of this application possesses both excellent mechanical strength and plasticity.

[0071] In this article, electroplated copper foil refers to copper foil prepared by electroplating. Copper foil can also be prepared by rolling in the prior art; copper foil prepared by rolling is referred to as rolled copper foil in this article. Electroplated copper foil and rolled copper foil have different physical properties and grain structures. Specifically, rolled copper foil has better surface uniformity and flatness than electrolytic copper foil, but its purity is lower. Rolled copper foil mainly consists of transverse grains or is predominantly composed of transverse grains, while electroplated copper foil has a columnar grain structure. Electroplated copper foil and rolled copper foil can be easily distinguished by EBSD testing.

[0072] In this article, the term "yield-to-tensile strength ratio" refers to the ratio of yield strength to tensile strength, which reflects the ability of copper foil to form and maintain a certain shape after processing or being subjected to stress, i.e., formability.

[0073] In this article, the term "yield strength" refers to the yield limit of a material when it yields. To measure the yield characteristics of a material, the stress value at which permanent residual plastic deformation equals a certain value (generally 0.2% of the original length) is defined as the yield strength.

[0074] In this paper, the term "tensile strength" refers to the maximum load-bearing capacity of a specimen when it is continuously loaded until it breaks, which is also the stress value of permanent residual plastic deformation.

[0075] The yield strength ratio is the ratio of a metal's yield strength to its tensile strength. Yield strength is the stress at which a metal begins to undergo plastic deformation under stress, while tensile strength is the maximum stress a metal can withstand during tension. A lower yield strength ratio indicates that the metal can withstand greater plastic deformation after yielding, exhibiting better ductility and toughness. Increasing the yield strength ratio can reduce the strain hardening ability of copper foil grains and decrease its resistance to lateral bending. Conversely, decreasing the yield strength ratio can increase the strain hardening ability of copper foil grains and improve its plasticity. Copper foil with a suitable yield strength ratio exhibits excellent mechanical strength and plasticity.

[0076] In this paper, the term "elongation at break" refers to the ratio of the length change of a material from its original length to its original length after plastic deformation under stress. It is usually expressed as a percentage and is an important parameter for measuring the deformation capacity of a material under stress during tension. Copper foil with a suitable elongation at break exhibits good plasticity.

[0077] In this application, the yield strength, tensile strength, and elongation at break of the copper foil can be tested using methods known in the art, such as according to GB / T 5230-1995 "Electrolytic Copper Foil" standard. As an example, at least four specimens with a test area length of 50±0.25 mm and a width of 15±0.25 mm are cut. The specimens are continuously loaded at a tensile speed of 50±0.5 mm / min at room temperature (10℃-30℃) until breakage. The tensile strength of the specimen is obtained by dividing the maximum load by the cross-sectional area of ​​the specimen. The cross-sectional area of ​​the specimen can be calculated by dividing the specimen mass by the product of the specimen length and density. The elongation at break can be calculated using the displacement method after the above test. The test area refers to the detection area during instrument testing. Considering that the specimen may need to be fixed by a clamp during testing, the length and width of the specimen can be greater than the length and width of the test area.

[0078] In some embodiments, the yield strength ratio of the copper foil is 0.55-0.72, 0.55-0.70, or 0.60-0.75. In some embodiments, the yield strength ratio of the copper foil is 0.55, 0.58, 0.60, 0.62, 0.65, 0.68, 0.70, 0.72, or 0.75, or any value within any two of the above values.

[0079] In some embodiments, the elongation at break of the copper foil is 5.5%-7.3%, 5.5%-7.0%, 6.0%-7.5%, or 6.0%-7.3%. In some embodiments, the elongation at break of the copper foil is 5.5%, 5.7%, 6.0%, 6.2%, 6.5%, 6.8%, 7.0%, 7.3%, or 7.5%, any value within any two of the above values ​​or any value within the range.

[0080] In some embodiments, the copper foil has a yield strength ratio of 0.55-0.72 and an elongation at break of 5.5%-7.3%, which is beneficial for the copper foil to have both good mechanical properties and high plasticity.

[0081] In some embodiments, the tensile strength of the copper foil is 500 MPa - 650 MPa, and may be optionally 510 MPa - 610 MPa. In some embodiments, the tensile strength of the copper foil is 500 MPa, 550 MPa, 580 MPa, 600 MPa, 620 MPa, 650 MPa, the range between any two of the above values, or any value within the range. A tensile strength within the above range is beneficial for the copper foil to maintain good plasticity without excessively reducing the mechanical strength of the copper foil.

[0082] In some embodiments, the average grain size of the copper foil grains is 0.2 μm - 0.7 μm, and may be optionally 0.3 μm - 0.6 μm, 0.3 μm - 0.5 μm, 0.4 μm - 0.6 μm, 0.4 μm - 0.5 μm. In some embodiments, the average grain size of the copper foil grains is 0.2 μm, 0.25 μm, 0.3 μm, 0.35 μm, 0.4 μm, 0.45 μm, 0.5 μm, 0.55 μm, 0.6 μm, 0.65 μm, 0.7 μm, the range between any two of the above values, or any value within the range.

[0083] In this article, the average grain size of the copper foil grains refers to the grain size in the inverse pole figure plane distribution map obtained by the electron backscatter diffraction (EBSD) test of the copper foil cross-section. Through the imageJ analysis software supporting the Oxford C-Nano+ electron backscatter diffraction instrument, the grain size in the copper foil cross-section is statistically analyzed, and a quantity distribution map is made. The equivalent circle diameter of the grains is used as the grain size, and the average grain size of the grains obtained by fitting with a skewed distribution is adopted.

[0084] In some embodiments, the minimum grain size of the copper foil grains is 0.1 μm - 0.3 μm, and may be optionally 0.1 μm - 0.2 μm, 0.15 μm - 0.25 μm, 0.2 μm - 0.3 μm. In some embodiments, the minimum grain size of the copper foil grains is 0.1 μm, 0.15 μm, 0.2 μm, 0.25 μm, 0.3 μm, the range between any two of the above values, or any value within the range.

[0085] In this article, the minimum grain size of the copper foil grains refers to the grain size in the inverse pole figure plane distribution map obtained by the electron backscatter diffraction (EBSD) test of the copper foil cross-section. Through the imageJ analysis software supporting the Oxford C-Nano+ electron backscatter diffraction instrument, the grain size in the copper foil cross-section is statistically analyzed, and a quantity distribution map is made. The equivalent circle diameter of the grains is used as the grain size, and a skewed distribution is adopted for fitting. In the statistical results, the smallest grain size is the minimum grain size of the copper foil grains.

[0086] In some embodiments, the maximum grain size of the copper foil is 2 μm - 4 μm, and may be optionally 2.3 μm - 3.5 μm, 2 μm - 3 μm, 2.5 μm - 3.0 μm. In some embodiments, the maximum grain size of the copper foil is 2.0 μm, 2.2 μm, 2.4 μm, 2.6 μm, 2.8 μm, 3.0 μm, 3.2 μm, 3.4 μm, 3.6 μm, 3.8 μm, 4.0 μm, the range between any two of the above values or any value within the range.

[0087] In this article, the maximum grain size of the copper foil refers to the grain size in the inverse pole figure plane distribution map obtained by the electron backscatter diffraction (EBSD) test of the copper foil cross-section. The grain size in the copper foil cross-section is statistically analyzed by the imageJ analysis software supporting the Oxford C-Nano+ electron backscatter diffraction instrument to make a quantity distribution map. The equivalent circle diameter of the grain is used as the grain size, and the skewed distribution is used for fitting. In the statistical results, the largest grain size is the maximum grain size of the copper foil grains.

[0088] The grain size span between the maximum grain size and the minimum grain size is the difference between the maximum grain size and the minimum grain size.

[0089] In some embodiments, the grain size span between the maximum grain size and the minimum grain size of the copper foil is 2 μm - 4 μm, and may be optionally 2 μm - 3.5 μm, 2.5 μm - 3.5 μm, 2.5 μm - 3.0 μm. In some embodiments, the grain size span between the maximum grain size and the minimum grain size of the copper foil is 2 μm, 2.2 μm, 2.4 μm, 2.6 μm, 2.8 μm, 3 μm, 3.2 μm, 3.4 μm, 3.6 μm, 3.8 μm, 4.0 μm, the range between any two of the above values or any value within the range.

[0090] A suitable grain size span can fully accumulate geometrically necessary dislocations, increase the grain dislocation density, enhance the resistance to grain dislocation movement and the occurrence of concentrated stress during the deformation of the copper foil, thereby strengthening the copper foil strength and improving the brittleness of the copper foil; it can also enhance the resistance to coordinated slip of grains, improve the mechanical strength of the copper foil while improving the deformation stability, meet the usage requirements of high-energy density batteries or high-expansion batteries, and improve the safety of secondary batteries.

[0091] In the copper foil, large-sized grains have higher mobility of grain dislocations and thus high plasticity. Small-sized grains increase the resistance to the movement of grain dislocations due to the increased grain boundary density, improving the mechanical strength of the copper foil. Therefore, metal materials with different grain sizes exhibit obvious differences in work hardening. The change in the grain size of the copper foil enhances the difference in work hardening of the grains, strengthens the ability to inhibit strain localization, reduces the occurrence of concentrated stress, and while increasing the mechanical strength of the copper foil, reduces the brittleness of the copper foil. In addition, it is also conducive to inducing a higher density of geometrically necessary dislocations, increasing the resistance to grain slip movement and improving the plasticity of the copper foil. This helps to extend the elastic-plastic transition stage at the initial stage of copper foil deformation, thereby obtaining higher additional strengthening and work hardening, improving the deformation stability of the copper foil, and enhancing the safety and service life of secondary batteries.

[0092] The average grain diameter, maximum grain diameter, minimum grain diameter of the grains in the copper foil, and the grain diameter span between the maximum grain diameter and the minimum grain diameter can be measured by methods known in the art. As an example, by combining an electron backscatter diffraction (EBSD) instrument and a scanning electron microscope to measure the cross-section of the copper foil, an inverse pole figure plane distribution map is obtained. Using the imageJ analysis software equipped with the Oxford C-Nano+ electron backscatter diffraction instrument, the grain diameters in its cross-section are statistically analyzed to make a quantity distribution map, as shown in Figures 14 - 17. Taking the equivalent circle diameter of the grains as the grain diameter, a skewed distribution is used for fitting to obtain the average grain diameter, maximum grain diameter, and minimum grain diameter of the grains, and the grain diameter span between the maximum grain diameter and the minimum grain diameter is calculated.

[0093] In some embodiments, the thickness of the copper foil is 4 μm - 8 μm. In some embodiments, the thickness H of the copper foil is 4.5 μm - 8 μm, and can be optionally 5 μm - 8 μm. In some embodiments, the thickness H of the copper foil is 4 μm, 4.5 μm, 5 μm, 5.5 μm, 6 μm, 6.5 μm, 7 μm, 7.5 μm, 8 μm, any range between the above two values or any value within the range.

[0094] In the present application, the thickness of the copper foil can be measured by methods known in the art. As an example, a sample of 20×15 cm 2 is cut, and the cut sample strip is placed on an electronic balance for weighing to obtain the weight of the sample strip. Then, based on the density ρ of the copper foil being 8.96 g / cm 3 the volume of the sample strip is calculated. Since the length and width of the sample strip are known, the thickness of the sample strip can be calculated therefrom.

[0095] This copper foil has a low thickness and light weight, which helps to reduce the weight of the battery and further improve the energy density.

[0096] [Preparation Method]

[0097] The second aspect of this application provides a method for preparing a current collector, including an electroplating method for preparing electroplated copper foil. The electroplating method includes applying a linear oscillating current to an electrolyte to reduce and deposit copper ions in the electrolyte to form copper foil. Under test conditions of 10℃-30℃, sample length × width of (50±0.25mm) × (15±0.25mm), and tensile speed of 50±0.5mm / min, the yield strength ratio of the copper foil is 0.55-0.75 and the elongation at break is 5.5%-7.5%.

[0098] In this article, the term "electroplating" refers to a method that uses the principle of electrolysis to deposit metal or alloy onto the surface of a workpiece to form a metal layer.

[0099] In this paper, the term "linear oscillating current" refers to an oscillating current with a linear current waveform that changes periodically and linearly.

[0100] Compared to the existing rolling method, the electroplating process is mature and simple, with low equipment requirements and low manufacturing costs. The copper foil produced not only has excellent mechanical strength and good deformation stability, but also helps to reduce the manufacturing cost of secondary batteries.

[0101] In existing electroplating methods for preparing copper foil, direct current is typically used to deposit copper. Adjusting the magnitude of the direct current can result in copper foil with fine and uniform grains, thereby enhancing its strength. However, this reduces the plasticity of the copper foil. Due to the reduced ability to suppress strain localization, the copper foil is prone to stress concentration during deformation, resulting in low bending resistance and a risk of brittle fracture. The preparation method provided in this application uses a linear oscillating current. By controlling and adjusting the formation and growth of reduced copper ions through the magnitude of the current, the grain size is adjusted, and a heterogeneous structure of the copper foil is formed, thus maintaining excellent plasticity while enhancing the strength of the copper foil.

[0102] In some embodiments, the peak value of the linear oscillating current is 35KA-45KA, optionally 40KA-45KA. In some embodiments, the peak value of the linear oscillating current is 35KA, 38KA, 39KA, 40KA, 43KA, or 45KA, any two of the above values ​​or any value within the range mentioned above.

[0103] In some embodiments, the valley value of the linear oscillating current is 15KA-25KA, optionally 20KA-25KA. In some embodiments, the valley value of the linear oscillating current is 15KA, 18KA, 19KA, 20KA, 23KA, or 35KA, any two of the above values ​​or any value within the range mentioned above.

[0104] In some embodiments, the range of the linear oscillating current is 20KA-45KA, and can be selected as 20KA-40KA.

[0105] In some embodiments, the period of the linear oscillating current is 10ms-500ms, and can be selected as 20ms-50ms or 50ms-100ms. In some embodiments, the period of the linear oscillating current is 20ms, 30ms, 40ms, 50ms, 60ms, 70ms, 80ms, 100ms, 150ms, 200ms, 250ms, 300ms, 350ms, 400ms, 450ms, or 500ms, or any value within any two of the above values ​​or any value within the range.

[0106] In this article, the term "peak value" refers to the maximum current value of a linear oscillating current, typically the value at the crest of a linear current waveform. Similarly, the term "valley value" refers to the minimum current value of a linear oscillating current, typically the value at the trough of a linear current waveform.

[0107] In this article, the term "cycle of change" refers to the time between two adjacent peaks or troughs in a linear current waveform, measured in milliseconds (ms).

[0108] During copper ion deposition, increasing the current accelerates the deposition rate, resulting in fine copper grains; decreasing the current reduces the deposition rate, promoting the formation of large, well-ordered grains. Through continuous variation of the linear oscillating current, the size of the deposited copper grains changes.

[0109] Furthermore, adjusting the peak value helps control the average grain size of fine grains, improving the grain boundary tortuosity degradation caused by reduced grain size, strengthening the grains while improving brittleness, and enhancing the bending resistance of the copper foil. Adjusting the current valley value can control the average grain size of large grains in the copper foil, reducing or avoiding the strength weakening and excessive plasticity caused by the increase in the grain size of large grains. Adjusting the variation period of the sinusoidal current helps to regulate the grain size span between the largest and smallest grains in the copper foil, ensuring sufficient grain size distribution between large and small grains. This allows for the accumulation of more geometrically necessary dislocations and differences in work hardening ability, increasing the resistance to dislocation movement and grain co-slip, and enhancing the ability to suppress local strain. This allows the copper foil to improve brittleness while enhancing mechanical strength.

[0110] In some implementations, as shown in Figure 7, the linear oscillating current varies in the range of 20KA-45KA, with a variation period of 50ms.

[0111] In some embodiments, the preparation method is a continuous production method.

[0112] In some embodiments, the preparation method is a roller deposition method. Its working principle is that the cathode roller is connected to the negative terminal of the power supply, and the anode tank is connected to the positive terminal. When the electrolyte containing copper ions enters the anode tank, an electric field is formed between the positive and negative electrodes. Under the action of the electric field, copper ions migrate to the surface of the cathode roller and are deposited. The deposited copper foil is peeled off from the cathode roller and wound onto another roller. The electrolyte is continuously added and circulated, and copper ions are continuously deposited on the cathode roller under the action of the electric field, continuously peeled off, and wound onto the winding shaft. This preparation method enables large-scale continuous production of copper foil, providing possibilities for industrial applications.

[0113] In some embodiments, the cathode electrode is a titanium roller or a titanium plate.

[0114] In some embodiments, the anode electrode is a titanium substrate plate, such as a titanium anode (iridium-based) with a DSA (Dimensionally Stable Anode) coating.

[0115] In some embodiments, the distance between the cathode electrode and the anode electrode is 10mm-20mm. In some embodiments, the distance between the cathode electrode and the anode electrode is 15mm, 16mm, 17mm, 18mm, 19mm, or 20mm, or any value within any two of the above values.

[0116] In some embodiments, the electroplating deposition temperature is 45°C-60°C. In some embodiments, the deposition temperature can be selected from 45°C, 50°C, 55°C, 60°C, any two of the above values, or any value within the range.

[0117] In some embodiments, the electroplating deposition time is greater than or equal to 80s, and can be selected from 80s to 300s. In some embodiments, the deposition time can be selected from any two of the above values ​​or any value within the range of the above values, such as 80s, 100s, 200s, 220s, 240s, 280s, 300s, 400s, 500s, 800s, or 1000s.

[0118] In some embodiments, the electrolyte includes: a leveling agent comprising collagen; a wetting agent comprising one or more of polyethylene glycol and hydroxyethyl cellulose; and a brightening agent comprising sodium polydithiopropane sulfonate.

[0119] In this article, the term "leveling agent" refers to a substance added to the electrolyte that can improve the smoothness of the coating. It can adhere to the tip of the copper foil with a fast deposition rate, inhibit grain growth, balance the growth rate of pits and tips, and improve the smoothness of the copper foil.

[0120] In this article, the term "wetting agent" refers to a substance used to reduce the interfacial tension between the electrolyte and the electrode, thereby improving the adhesion of the coating to the substrate. Wetting agents can enhance the wettability of the electrolyte to the substrate, and the wettability of the electrolyte on the cathode is sufficient to enable rapid electrodeposition with high current, thereby increasing the nucleation rate of copper foil and reducing the grain size in the copper foil.

[0121] In this article, the term "brightener" refers to a substance that improves the smoothness of the coating and reduces surface roughness. Brighteners can make the grain size of copper foil smaller and reduce the surface roughness of the copper foil, thereby improving the smoothness of the surface.

[0122] In some embodiments, the electrolyte comprises 10-300 parts by weight of a leveling agent, 20-200 parts by weight of a wetting agent, and 50-200 parts by weight of a brightening agent.

[0123] Furthermore, the electrolyte further includes 60-100 parts by weight of copper ions (based on the atomic mass of copper) and 10-100 parts by weight of chloride ions (based on the atomic mass of chloride). Furthermore, the electrolyte further includes 60-110 parts by weight of sulfuric acid.

[0124] In the electrolyte, copper ions provide the copper source for the formation of the copper foil. The use of chloride ions in conjunction with a wetting agent can further improve the electrodeposition process. Sulfuric acid not only dissolves the copper material but also maintains an acidic environment in the electrolyte to facilitate the reduction of copper ions.

[0125] In some embodiments, the concentration of collagen in the electrolyte is 10-300 mg / L, optionally 90-120 mg / L. In some embodiments, the concentration of collagen in the electrolyte is 10 mg / L, 30 mg / L, 50 mg / L, 80 mg / L, 100 mg / L, 120 mg / L, 150 mg / L, 180 mg / L, 200 mg / L, or 300 mg / L, any range between any two of the above values ​​or any value within the range.

[0126] In some embodiments, the wetting agent includes hydroxyethyl cellulose and polyethylene glycol.

[0127] In some embodiments, the concentration of polyethylene glycol in the electrolyte is 10-200 mg / L, optionally 20-80 mg / L. In some embodiments, the concentration of polyethylene glycol in the electrolyte is 10 mg / L, 20 mg / L, 30 mg / L, 40 mg / L, 50 mg / L, 60 mg / L, 70 mg / L, 80 mg / L, 100 mg / L, 150 mg / L, or 200 mg / L, or any value within any two of the above values.

[0128] In some embodiments, the concentration of hydroxyethyl cellulose in the electrolyte is 10-100 mg / L, optionally 10-80 mg / L. In some embodiments, the concentration of hydroxyethyl cellulose in the electrolyte is 10 mg / L, 20 mg / L, 30 mg / L, 40 mg / L, 50 mg / L, 60 mg / L, 70 mg / L, 80 mg / L, 90 mg / L, or 100 mg / L, any range between any two of the above values ​​or any value within the range.

[0129] In some embodiments, the concentration of the sodium polydisulfide dipropane sulfonate in the electrolyte is 50-200 mg / L, optionally 50-150 mg / L. In some embodiments, the concentration of the sodium polydisulfide dipropane sulfonate in the electrolyte is 50 mg / L, 80 mg / L, 90 mg / L, 100 mg / L, 110 mg / L, 120 mg / L, 150 mg / L, 180 mg / L, or 200 mg / L, any range between any two of the above values ​​or any value within the range.

[0130] Sodium polydisulfide dipropane sulfonate is adsorbed onto the copper cathode surface via thiol functional groups. The terminal sulfonate anions capture hydrated copper ions in the electrolyte, thereby disrupting their hydration. It also interacts with chloride ions adsorbed on the cathode surface, allowing electrons to be transferred to the captured copper ions via chloride ions. This significantly increases the electrochemical reduction rate of copper ions, refines the grain size, and strengthens the material.

[0131] In some embodiments, the electrolyte comprises: collagen at a concentration of 10-300 mg / L, polyethylene glycol at a concentration of 20-100 mg / L, hydroxyethyl cellulose at a concentration of 10-100 mg / L, and sodium polydisulfide dipropane sulfonate at a concentration of 50-200 mg / L.

[0132] In some embodiments, the electrolyte comprises: collagen at a concentration of 90-120 mg / L, polyethylene glycol at a concentration of 20-80 mg / L, hydroxyethyl cellulose at a concentration of 10-80 mg / L, and sodium polydisulfide dipropane sulfonate at a concentration of 50-150 mg / L.

[0133] In some embodiments, the electrolyte comprises chloride ions (calculated as chloride atoms) at a concentration of 10-100 mg / L, and optionally, the chloride ion concentration is 20-80 mg / L.

[0134] In some embodiments, the electrolyte comprises sulfuric acid with a concentration of 60-110 g / L, or optionally, sulfuric acid with a concentration of 80-100 g / L.

[0135] In some embodiments, the electrolyte comprises copper ions at a concentration of 60-100 g / L, optionally at a concentration of 60-90 g / L.

[0136] In some embodiments, the electrolyte comprises: collagen at a concentration of 10-300 mg / L, polyethylene glycol at a concentration of 20-100 mg / L, sodium polydisulfide sulfonate at a concentration of 50-200 mg / L, chloride ions at a concentration of 10-100 mg / L, copper ions at a concentration of 60-100 g / L, and sulfuric acid at a concentration of 60-110 g / L.

[0137] In some embodiments, the electrolyte comprises: collagen at a concentration of 90-120 mg / L, polyethylene glycol at a concentration of 20-80 mg / L, sodium polydisulfide dipropane sulfonate at a concentration of 50-150 mg / L, chloride ions at a concentration of 20-80 mg / L, copper ions at a concentration of 60-90 g / L, and sulfuric acid at a concentration of 80-100 g / L.

[0138] The method provided in this application, through the synergistic effect of the electrolyte and electroplating parameters, helps to form a dense, flat copper foil with continuously varying grain size. This copper foil exhibits excellent yield strength ratio and elongation at break, significantly improved tensile strength and bending resistance, and good mechanical strength and deformation stability, which is beneficial for improving the safety performance of high-energy-density or high-expansion batteries. Furthermore, the preparation method can achieve large-scale manufacturing, showing promise for industrial applications.

[0139] [Negative electrode plate]

[0140] As an example of a negative electrode sheet, the negative current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative current collector.

[0141] In some embodiments, the negative electrode current collector can be the current collector described in any embodiment of the first aspect of this application, thereby providing a material basis for improving the energy density of the secondary battery and helping to improve the safety of the secondary battery.

[0142] In some embodiments, the negative electrode active material includes one of artificial graphite, natural graphite, soft carbon, hard carbon, and mesophase carbon microspheres. In some embodiments, the negative electrode active material includes artificial graphite.

[0143] In some embodiments, the negative electrode film layer may further include other negative electrode active materials besides the graphite material described above. In some embodiments, the other negative electrode active materials include, but are not limited to, one or more of conventional natural graphite, artificial graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate. The silicon-based materials may include one or more of elemental silicon, silicon oxide, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based materials may include one or more of elemental tin, tin oxide, and tin alloys.

[0144] In some embodiments, the negative electrode film layer may optionally include a binder. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0145] In some embodiments, the negative electrode also includes a conductive agent. The conductive agent includes one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0146] In some embodiments, the conductive agent includes carbon black. In some embodiments, the conductive agent includes carbon nanotubes. In some embodiments, the conductive agent includes both carbon black and carbon nanotubes. The conductive agent is widely available, has excellent conductivity, and is beneficial for controlling the manufacturing cost of secondary batteries and improving the conductivity of the negative electrode.

[0147] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0148] In some embodiments, the negative electrode sheet can be prepared by dispersing the components used to prepare the negative electrode sheet, such as the negative electrode active material, conductive agent, binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto the negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0149] [Positive electrode plate]

[0150] The positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector, the positive electrode film layer including a positive electrode active material.

[0151] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0152] In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0153] In some embodiments, the positive electrode active material may be a known battery positive electrode active material. As an example, the positive electrode active material may include at least one of the following materials: lithium phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, this application is not limited to these materials, and other conventional materials that can be used as battery positive electrode active materials may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides include, but are not limited to, lithium cobalt oxides (such as LiCoO2), lithium nickel oxides (such as LiNiO2), lithium manganese oxides (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, and lithium nickel cobalt manganese oxides (such as LiNi). 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also known as NCM) 333 LiNi 0.5 Co 0.2 Mn 0.3 O2 (also known as NCM) 523 LiNi 0.5 Co 0.25 Mn 0.25 O2 (also known as NCM) 211 LiNi 0.6 Co 0.2 Mn 0.2 O2 (also known as NCM) 622 LiNi 0.8 Co 0.1 Mn 0.1 O2 (also known as NCM) 811 ), lithium nickel cobalt aluminum oxide (such as LiNi) 0.85 Co 0.15 Al 0.05At least one of O2 and its modified compounds. Examples of lithium phosphates with an olivine structure include, but are not limited to, lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), lithium iron phosphate and carbon composites, lithium manganese phosphate (such as LiMnPO4), lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, and lithium manganese iron phosphate and carbon composites.

[0154] In some embodiments, the positive electrode film layer may optionally include a binder. As an example, the binder may include at least one selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0155] In some embodiments, the positive electrode film may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0156] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, conductive agent, binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0157] [Electrolytes]

[0158] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This application does not impose specific restrictions on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be liquid, gel, or entirely solid.

[0159] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0160] In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0161] In some embodiments, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0162] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0163] [Isolation membrane]

[0164] In some embodiments, the secondary battery also includes a separator. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0165] In some embodiments, the material of the separator can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0166] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0167] In some embodiments, the secondary battery may include an outer packaging. This outer packaging may be used to encapsulate the electrode assembly and electrolyte described above.

[0168] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the secondary battery can also be a soft pack, such as a pouch. The material of the soft pack can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0169] In addition, the secondary battery, battery module, battery pack and power device of this application will be described below with appropriate reference to the accompanying drawings.

[0170] In one embodiment of this application, a secondary battery is provided.

[0171] This application does not impose any particular limitation on the shape of the secondary battery; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 1 shows a square-structured secondary battery 5 as an example.

[0172] In some embodiments, referring to FIG2, the outer packaging may include a housing 51 and a cover plate 53. The housing 51 may include a bottom plate and side plates connected to the bottom plate, the bottom plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover plate 53 can be placed over the opening to close the receiving cavity. A positive electrode, a negative electrode, and a separator can be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The secondary battery 5 may contain one or more electrode assemblies 52, which can be selected by those skilled in the art according to specific practical needs.

[0173] In some implementations, the secondary batteries can be assembled into a battery module, and the number of secondary batteries contained in the battery module can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery module.

[0174] Figure 3 shows a battery module 4 as an example. Referring to Figure 3, in the battery module 4, multiple secondary batteries 5 can be arranged sequentially along the length of the battery module 4. Of course, they can also be arranged in any other manner. Furthermore, the multiple secondary batteries 5 can be fixed in place using fasteners.

[0175] Optionally, the battery module 4 may also include a housing with a receiving space in which a plurality of secondary batteries 5 are received.

[0176] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0177] Figures 4 and 5 show a battery pack 1 as an example. Referring to Figures 4 and 5, the battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper box 2 and a lower box 3, with the upper box 2 covering the lower box 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0178] Furthermore, embodiments of this application also provide an electrical device, which includes at least one of a secondary battery, a battery module, or a battery pack provided in any embodiment of this application. The secondary battery, battery module, or battery pack can be used as a power source for the electrical device, or as an energy storage unit for the electrical device. The electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0179] As the electrical device, a secondary battery, battery module, or battery pack can be selected according to its usage requirements.

[0180] Figure 6 shows an example of an electrical device. This device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. To meet the high power and high energy density requirements of the secondary battery for this device, a battery pack or battery module can be used.

[0181] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a rechargeable battery as their power source.

[0182] Example

[0183] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0184] Example 1

[0185] Preparation of copper foil

[0186] Copper plates or wires with a purity of 99.9% or higher were dissolved in 98% sulfuric acid to prepare a copper sulfate solution. This solution was used as the copper source, and an electrolyte was prepared by adding additives and hydrochloric acid at 60°C. The resulting electrolyte had a pH of 3.5 and contained the following components: collagen (90 mg / L), polyethylene glycol (50 mg / L), hydroxyethyl cellulose (30 mg / L), chloride ions (30 mg / L), sodium polydithiopropane sulfonate (75 mg / L), copper ions (90 g / L), sulfuric acid (100 g / L), and the remainder was deionized water.

[0187] A linear current waveform is used to periodically apply current to a polished titanium cathode roller, while the anode electrode is a titanium substrate plate. The area of ​​the titanium roller located in the electrolyte is 0.3 dm². 2 The titanium roller rotates at a speed of 2 m / min, and the applied current ranges from a minimum of 20 kA to a maximum of 45 kA, with a cycle of 50 ms. The cathode-anode distance is 20 mm, and the deposition temperature is 60 °C. The electroplating time is 224 s, during which copper foil with a thickness of 6 μm is deposited on the titanium roller.

[0188] Examples 2-5

[0189] The preparation process of Examples 2-5 is basically similar to that of Example 1, but the minimum current is adjusted to 25KA, 30KA, 35KA and 40KA respectively.

[0190] Comparative Example 1

[0191] The preparation process of Comparative Example 1 is basically similar to that of Example 1, but a direct current of 45 kA is used to prepare copper foil.

[0192] Performance testing

[0193] (1) Mechanical property testing

[0194] According to GB / T 5230-1995 "Electrolytic Copper Foil", tensile specimens with a length L0 of 50 mm and a width of 15 mm were cut at room temperature (10℃-30℃). The tensile properties were tested using a universal testing machine at 25℃, with the tensile rate set to 50 mm / min.

[0195] Then the cross-sectional area of ​​the stretched spline Where ρ is 8.96 g / cm³ 3 The unit of m is gram, and the unit of L0 is centimeter.

[0196] The specimen is continuously loaded until it breaks (resulting in permanent residual plastic deformation). The maximum load F is read from the force measuring plate or the tensile curve, and then calculated according to the formula. Calculate the tensile strength σ b .

[0197] Yield strength σ 0.2 The stress required to produce permanent residual plastic deformation equal to 0.2% of the original length.

[0198] The yield strength ratio is equal to the yield strength σ. 0.2 With tensile strength σ b The ratio of .

[0199] The distance between the two lines after the specimen breaks is L1, which is measured on the specimen or read from the tensile curve. L1 can be measured using the linear method or the displacement method, according to the formula. Calculate the fracture elongation ε.

[0200] (2) Brittleness test

[0201] Cut the copper foil into test strips with a width of 15 mm, fold it in half, roll it with a 2 kg roller, then turn it over and roll it again until a light transmission point appears on the copper foil under a 2000 lux lamp, and record the number of folding times.

[0202] (3) Grain characteristic test of copper foil

[0203] Observe the cross-section of the copper foil by using electron backscatter diffraction (EBSD) combined with a scanning electron microscope. The model of the electron backscatter diffraction instrument is Oxford C-Nano+, and obtain the inverse pole figure plane distribution map. Statistically analyze the equivalent circle diameter of the grains through the imageJ analysis software supporting the Oxford C-Nano+ electron backscatter diffraction instrument, and determine the average grain diameter, the maximum grain diameter, the minimum grain diameter, and the grain diameter span between the maximum grain diameter and the minimum grain diameter.

[0204] The test results of the mechanical characteristics of the copper foils prepared in Examples 1-5 and Comparative Example 1 are shown in Table 1:

[0205] Table 1

[0206] As can be seen from the tensile curves of Examples 1-5 and Figures 8-12, within the range of linear current change from 20 KA to 45 KA, the yield ratio of the prepared copper foil is within the range of 0.55-0.75, and the fracture elongation is within the range of 5.5%-7.5%. The copper foil has both excellent yield ratio and fracture elongation. The copper foil has good mechanical strength and plasticity, which significantly improves the number of folding times of the copper foil.

[0207] At the same time, the tensile strength of the copper foils prepared in Examples 1-5 is within the range of 518 MPa - 603 MPa, and the yield strength is within the range of 282 MPa - 436 MPa, indicating that the copper foil has good mechanical strength and plasticity.

[0208] Comparing Examples 1-5 with Comparative Example 1 and Figure 13, under the condition of using a DC current of 45 KA, the tensile strength and yield ratio of the prepared copper foil are close to those of the copper foil prepared under the condition of linear oscillating current (20 KA - 40 KA), but the fracture elongation and the number of folding times are significantly worse, and the brittleness defect of the copper foil is serious. Compared with the copper foil prepared by DC current deposition, the copper foil prepared by linear oscillating current deposition improves the brittleness defect of the copper foil at high tensile strength, significantly improves the anti-bending performance, and has better plasticity and deformation stability.

[0209] The test results of the grain characteristics of the copper foils in Examples 1-2 and Comparative Example 1 are shown in Table 2:

[0210] Table 2

[0211] Figures 14-15 show the cross-sectional electron backscatter diffraction (EBSD) patterns and particle size distribution of the copper foil prepared in Example 1; Figures 16-17 show the cross-sectional electron backscatter diffraction (EBSD) patterns and particle size distribution of the copper foil prepared in Example 2; and Figures 18-19 show the cross-sectional electron backscatter diffraction (EBSD) patterns and particle size distribution of the copper foil prepared in Comparative Example 1. As can be seen from the figures and Table 2, the grain size range of the copper foils prepared in Examples 1 and 2 is significantly higher than that of Comparative Example 1. This improves the copper foil's ability to suppress strain localization, reduces the occurrence of concentrated stress, and increases grain slip resistance. While improving the mechanical strength of the copper foil, it also reduces its brittleness, resulting in excellent plasticity. This also corresponds to the test results of the number of folds of the copper foil; the number of folds of the copper foil in Example 1 is significantly better than that of the copper foil in Comparative Example 1.

[0212] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A current collector, characterized in that, The current collector comprises electroplated copper foil. Under test conditions of 10℃-30℃, sample length × width of (50±0.25mm) × (15±0.25mm), and tensile speed of 50±0.5mm / min, the yield strength ratio of the copper foil is 0.55-0.75 and the elongation at break is 5.5%-7.5%.

2. The current collector according to claim 1, characterized in that, The copper foil has a yield strength ratio of 0.55-0.72 and / or an elongation at break of 5.5%-7.3%.

3. The current collector according to claim 1 or 2, characterized in that, The tensile strength of the copper foil is 500MPa-650MPa.

4. The current collector according to any one of claims 1 to 3, characterized in that, The tensile strength of the copper foil is 510MPa-610MPa.

5. The current collector according to any one of claims 1 to 4, characterized in that, The maximum and minimum grain size of the copper foil crystals spans between 2μm and 4μm.

6. The current collector according to any one of claims 1 to 5, characterized in that, The maximum and minimum grain size of the copper foil grains range from 2.3 μm to 3 μm.

7. The current collector according to any one of claims 1 to 6, characterized in that, The copper foil satisfies at least one of the following conditions: (1) The average grain size of the copper foil is 0.2μm-0.7μm; (2) The minimum grain size of the copper foil is 0.1μm-0.3μm; (3) The maximum grain size of copper foil is 2μm-4μm.

8. The current collector according to any one of claims 1 to 7, characterized in that, The thickness of the copper foil is 4μm-8μm.

9. A method for preparing a current collector, characterized in that, The method includes preparing electroplated copper foil by electroplating, wherein the electroplating method involves applying a linear oscillating current to an electrolyte to reduce and deposit copper ions in the electrolyte to form copper foil. Under test conditions of 10℃-30℃, sample length × width of (50±0.25mm) × (15±0.25mm), and tensile speed of 50±0.5mm / min, the yield strength ratio of the copper foil is 0.55-0.75 and the elongation at break is 5.5%-7.5%.

10. The preparation method according to claim 9, characterized in that, The electroplating method satisfies one or more of the following conditions: (1) The variation range of the linear oscillating current is 20KA-45KA; (2) The period of the linear oscillating current is 10ms-500ms; (3) The distance between the cathode electrode and the anode electrode is 10mm-20mm; (4) The electroplating deposition temperature is 40℃-60℃; (5) The electroplating deposition time is greater than or equal to 80s.

11. The preparation method according to claim 9 or 10, characterized in that, The electrolyte comprises: A leveling agent, said leveling agent comprising collagen; A wetting agent, wherein the wetting agent comprises one or more of polyethylene glycol and hydroxyethyl cellulose; Brightening agent, wherein the brightening agent comprises sodium polydithiopropane sulfonate.

12. The preparation method according to claim 11, characterized in that, The electrolyte comprises: collagen at a concentration of 10-300 mg / L, polyethylene glycol at a concentration of 20-100 mg / L, hydroxyethyl cellulose at a concentration of 10-100 mg / L, and sodium polydisulfide dipropane sulfonate at a concentration of 50-200 mg / L.

13. The preparation method according to any one of claims 9 to 12, characterized in that, The electrolyte comprises: collagen at a concentration of 90-120 mg / L, polyethylene glycol at a concentration of 20-80 mg / L, hydroxyethyl cellulose at a concentration of 10-80 mg / L, and sodium polydisulfide dipropane sulfonate at a concentration of 50-150 mg / L.

14. The preparation method according to any one of claims 9 to 13, characterized in that, The electrolyte contains chloride ions at a concentration of 10-100 mg / L and copper ions at a concentration of 60-100 g / L.

15. An electrode sheet, characterized in that, The current collector includes the current collector prepared by any one of claims 1 to 8 or the current collector prepared by any one of claims 9 to 14.

16. A secondary battery, characterized in that, Includes the electrode as described in claim 15.

17. An electrical appliance, characterized in that, Includes the secondary battery as described in claim 16.

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